/****************************************************************************
 * net/bluetooth/iob/iob_alloc_qentry.c
 *
 *   Copyright (C) 2014, 2016-2017 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <semaphore.h>
#include <assert.h>
#include <errno.h>

#include <tinyara/irq.h>
#include <tinyara/arch.h>
#include <tinyara/bluetooth/iob/iob.h>

#include "iob.h"

#if CONFIG_IOB_NCHAINS > 0

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: iob_alloc_qcommitted
 *
 * Description:
 *   Allocate an I/O buffer by taking the buffer at the head of the committed
 *   list.
 *
 ****************************************************************************/

static FAR struct iob_qentry_s *iob_alloc_qcommitted(void)
{
	FAR struct iob_qentry_s *iobq = NULL;
	irqstate_t flags;

	/* We don't know what context we are called from so we use extreme measures
	 * to protect the committed list:  We disable interrupts very briefly.
	 */

	flags = enter_critical_section();

	/* Take the I/O buffer from the head of the committed list */

	iobq = g_iob_qcommitted;
	if (iobq != NULL) {
		/* Remove the I/O buffer from the committed list */

		g_iob_qcommitted = iobq->qe_flink;

		/* Put the I/O buffer in a known state */

		iobq->qe_head = NULL;	/* Nothing is contained */
	}

	leave_critical_section(flags);
	return iobq;
}

/****************************************************************************
 * Name: iob_allocwait_qentry
 *
 * Description:
 *   Allocate an I/O buffer chain container by taking the buffer at the head
 *   of the free list.  This function is intended only for internal use by
 *   the IOB module.
 *
 ****************************************************************************/

static FAR struct iob_qentry_s *iob_allocwait_qentry(void)
{
	FAR struct iob_qentry_s *qentry;
	irqstate_t flags;
	int ret = OK;

	/* The following must be atomic; interrupt must be disabled so that there
	 * is no conflict with interrupt level I/O buffer chain container
	 * allocations.  This is not as bad as it sounds because interrupts will be
	 * re-enabled while we are waiting for I/O buffers to become free.
	 */

	flags = enter_critical_section();

	/* Try to get an I/O buffer chain container.  If successful, the semaphore
	 * count will bedecremented atomically.
	 */

	qentry = iob_tryalloc_qentry();
	while (ret == OK && qentry == NULL) {
		/* If not successful, then the semaphore count was less than or equal
		 * to zero (meaning that there are no free buffers).  We need to wait
		 * for an I/O buffer chain container to be released when the
		 * semaphore count will be incremented.
		 */

		ret = sem_wait(&g_qentry_sem);
		if (ret < 0) {
			/* EINTR is not an error!  EINTR simply means that we were
			 * awakened by a signal and we should try again.
			 *
			 * REVISIT:  Many end-user interfaces are required to return
			 * with an error if EINTR is set.  Most uses of this function
			 * is in internal, non-user logic.  But are there cases where
			 * the error should be returned.
			 */

			if (errno == EINTR) {
				/* Force a success indication so that we will continue looping. */

				ret = OK;
			}
		} else {
			/* When we wake up from wait successfully, an I/O buffer chain container was
			 * freed and we hold a count for one IOB.  Unless somehting
			 * failed, we should have an IOB waiting for us in the
			 * committed list.
			 */

			qentry = iob_alloc_qcommitted();
			DEBUGASSERT(qentry != NULL);

			if (qentry == NULL) {
				/* This should not fail, but we allow for that possibility to
				 * handle any potential, non-obvious race condition.  Perhaps
				 * the free IOB ended up in the g_iob_free list?
				 *
				 * We need release our count so that it is available to
				 * iob_tryalloc(), perhaps allowing another thread to take our
				 * count.  In that event, iob_tryalloc() will fail above and
				 * we will have to wait again.
				 */

				sem_post(&g_qentry_sem);
				qentry = iob_tryalloc_qentry();
			}
		}
	}

	leave_critical_section(flags);
	return qentry;
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: iob_alloc_qentry
 *
 * Description:
 *   Allocate an I/O buffer chain container by taking the buffer at the head
 *   of the free list. This function is intended only for internal use by
 *   the IOB module.
 *
 ****************************************************************************/

FAR struct iob_qentry_s *iob_alloc_qentry(void)
{
	/* Were we called from the interrupt level? */

	if (up_interrupt_context()) {
		/* Yes, then try to allocate an I/O buffer without waiting */

		return iob_tryalloc_qentry();
	} else {
		/* Then allocate an I/O buffer, waiting as necessary */

		return iob_allocwait_qentry();
	}
}

/****************************************************************************
 * Name: iob_tryalloc_qentry
 *
 * Description:
 *   Try to allocate an I/O buffer chain container by taking the buffer at
 *   the head of the free list without waiting for the container to become
 *   free. This function is intended only for internal use by the IOB module.
 *
 ****************************************************************************/

FAR struct iob_qentry_s *iob_tryalloc_qentry(void)
{
	FAR struct iob_qentry_s *iobq;
	irqstate_t flags;

	/* We don't know what context we are called from so we use extreme measures
	 * to protect the free list:  We disable interrupts very briefly.
	 */

	flags = enter_critical_section();
	iobq = g_iob_freeqlist;
	if (iobq) {
		/* Remove the I/O buffer chain container from the free list and
		 * decrement the counting semaphore that tracks the number of free
		 * containers.
		 */

		g_iob_freeqlist = iobq->qe_flink;

		/* Take a semaphore count.  Note that we cannot do this in
		 * in the orthodox way by calling sem_wait() or sem_trywait()
		 * because this function may be called from an interrupt
		 * handler. Fortunately we know at at least one free buffer
		 * so a simple decrement is all that is needed.
		 */

		g_qentry_sem.semcount--;
		DEBUGASSERT(g_qentry_sem.semcount >= 0);

		/* Put the I/O buffer in a known state */

		iobq->qe_head = NULL;	/* Nothing is contained */
	}

	leave_critical_section(flags);
	return iobq;
}

#endif							/* CONFIG_IOB_NCHAINS > 0 */
